1. Technical Field
The present invention is directed to a torque transfer assembly for a vehicle drive line and, more particularly, to a torque transfer assembly having a planetary differential.
2. Description
In order to optimize vehicle performance and driver confidence, it is desirable to provide independent torque control for each driving wheel at all times. Current torque control schemes are often of the xe2x80x9con demandxe2x80x9d type, providing controlled independent wheel movement only during certain driving circumstances. As a result, the operation of the system is not seamless and smooth and the benefits of independent wheel control are limited to specific slip conditions.
Further, currently used torque control systems commonly rely upon direct wet clutch/brake technology that also suffer from the inability to efficiently and effectively dissipate heat generated during operation. The build up of heat degrades performance and, particularly at extreme temperatures, can cause system shut-down. Yet other currently available systems shift gears to obtain a fixed ratio of wheel torques. However, these systems do not permit all of the input torque to be directed to a single wheel. Additionally, available torque control assemblies suffer from operational inefficiencies such as subjecting the torque control mechanisms to undesirably large forces.
Accordingly, the present invention is directed to a planetary differential for delivering torque to each of the driving wheels. The configuration of one of the disclosed embodiments of the planetary differential provides operational and functional benefits regarding torque distribution in an arrangement that minimizes the required robustness of the torque control mechanisms. Another embodiment of the present invention includes a control system that permits a variety of operating modes including a mode wherein the planetary differential provides self-regulating torque distribution between the left and right axle output shafts while providing a centralized torque controller that enables traction control, vehicle dynamic control and high degrees of controlled torque steering in special circumstances. A further benefit of the invention is that it permits transfer of all or any fraction of the available driveline torque to any single wheel or axle. Additional benefits of the planetary differential of the present invention include the easy conversion, use, or dissipation of accumulated energy in the torque control mechanisms and an overall configuration that permits the differential to be used in a variety of applications.
In view of the above, the present invention is directed to a torque transfer assembly including an input gear, a first output shaft, a second output shaft, a planetary differential and a torque control system. In one embodiment, the planetary differential includes first and second planetary gear set pairs each with inner and outer planetary gear sets. The torque control system includes first and second torque control mechanisms each having a control element rotating with one of the planetary gear set components as well as a controller communicating with the first and second control mechanisms and selectively controlling a resistance torque exerted by the first and second torque control mechanisms on the first and second control elements. In another embodiment, the torque control system includes a hydraulic control arrangement hydraulically intercoupling the first and second torque control mechanisms and a controller operable to selectively control the direction and amount of fluid flow in the hydraulic control arrangement and the resistance torque exerted by the first and second torque control mechanisms.
Further scope of applicability of the present invention will become apparent from the following detailed description, claims, and drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.